Many devices have been proposed for applying tension to fence wires that have stretched over time and become slack. A few of the better devices use small clips upon which slack, fence wire may be wound and retained for the remainder of the fence's life. Unfortunately, a typical clip employs only friction to hold in place the wire wound upon it. Thus, bumps from livestock, for example, can lead to the unwinding of slack wire from a conventional clip and to an ineffective fence.